Effect of IFN-γ on the kynurenine/tryptophan ratio in monolayer-cultured keratinocytes and a 3D reconstructed human epidermis model

Abstract Background Interferon-gamma (IFN-γ) represents a potent inducer for keratinocyte inflammatory and immune activationin vitro. Since tryptophan (trp) conversion to kynurenine (kyn) is involved in inflammation, the topical kyn/trp ratio may serve as a biomarker of skin inflammation. However, the trp metabolism in keratinocytes exposed to IFN-γ is not yet fully understood. Objective The aim of this study was to establish a human epidermis model in order to quantify cytokine and kyn/trp secretion from IFN-γ stimulated cells and tissues. Moreover, to compare the cell response of 2D-cultured keratinocytes and the 3D epidermis model. Methods Polycarbonate filters were used on which primary keratinocytes could attach and stratify in order to form the typical layers of reconstructed human epidermis (RHE). After IFN-γ treatment, secretion of kyn/trp was measured by high performance liquid chromatography. Gene and protein expression of indoleamine 2,3-dioxygenase 1 (IDO) was analyzed with real-time PCR and immunohistochemistry. The secretion of cytokines was quantified with ELISA. Results Trp catabolism to kyn was significantly increased (P  Conclusion Our results suggest that IFN-γ acts as an inducer of trp degradation preferentially in undifferentiated keratinocytes, indicated by the IDO expression in the basal layer of the RHE.